Control strategy for multiple kites on a single ground power unit

ABSTRACT

Methods and systems described herein relate to power generation control for an aerial vehicle. An example method may involve determining an asynchronous flight pattern for two or more aerial vehicles, where the asynchronous flight pattern includes a respective flight path for each of the two or more aerial vehicles; and operating each of the aerial vehicles in a crosswind flight substantially along its respective flight path, where each aerial vehicle generates electrical power over time in a periodic profile, and where the power profile of each aerial vehicle is out of phase with respect to the power profile generated by each of the other aerial vehicles.

CROSS REFERENCE TO RELATED APPLICATION

This disclosure is a continuation of U.S. patent application Ser. No.14/964,271 filed on Dec. 9, 2015, which is a continuation of, and claimspriority to U.S. Provisional patent application Ser. No. 62/260,246filed on Nov. 25, 2015, both of which are hereby incorporated byreference herein in their entirety.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Power generation systems may convert chemical and/or mechanical energy(e.g., kinetic energy) to electrical energy for various applications,such as utility systems. As one example, a wind energy system mayconvert kinetic wind energy to electrical energy.

SUMMARY

Methods and systems for managing power generation of a plurality ofaerial vehicles operating in a crosswind flight orientation aredescribed herein. Beneficially, embodiments described herein may help inreducing the overall peak power that may flow through a system. Further,embodiments described herein may help to reduce fluctuations in poweroutput.

In one aspect, a method may involve determining an asynchronous flightpattern for two or more aerial vehicles, where the asynchronous flightpattern includes a respective flight path for each of the two or moreaerial vehicles; and operating each of the aerial vehicles in acrosswind flight substantially along its respective flight path, whereeach aerial vehicle generates electrical power over time in a periodicprofile, and where the power profile of each aerial vehicle is out ofphase with respect to the power profile generated by each of the otheraerial vehicles.

In another aspect, a method may involve determining at least onepreferred phase differential between periodic power profiles generatedby two of two or more aerial vehicles; based at least on the at leastone preferred phase differential, determining an asynchronous flightpattern for the aerial vehicles, where the determined asynchronousflight pattern includes a respective flight path for each of the aerialvehicles; operating each of the aerial vehicles in a crosswind flightsubstantially along its respective flight path, where each aerialvehicle generates electrical power over time in a periodic profile, andwhere a phase differential between the power profiles generated by twoof the aerial vehicles is substantially the preferred phasedifferential.

In another aspect, a method may involve determining a deployment orderfor two or more aerial vehicles, where each aerial vehicle is configuredto operate substantially along a respective flight path to generateelectrical power; assigning the deployment order to the two or moreaerial vehicles; deploying the two or more aerial vehicles according tothe assigned deployment order, where deploying the two or more vehiclesaccording to the assigned deployment order includes: for an aerialvehicle in a first position of the deployment order, (i) deploying theaerial vehicle, (ii) operating the aerial vehicle in a loitering flight;for each aerial vehicle in the assigned deployment order between theaerial vehicle in the first position of the deployment order and anaerial vehicle in a last position of the deployment order, (i)determining that the preceding aerial vehicle in the assigned deploymentorder is operating in the loitering flight, (ii) deploying the aerialvehicle (iii) operating the aerial vehicle in a loitering flight; forthe aerial vehicle in the last position of the deployment order, (i)determining that the preceding aerial vehicle in the assigned deploymentorder is operating in the loitering flight, (ii) deploying the aerialvehicle, (iii) operating the aerial vehicle in a crosswind flight.

In another aspect, a system may include a shared ground power unit,where the shared ground power unit comprises a battery system; two ormore airborne wind turbines (AWTs), wherein each AWT includes: a tethercoupled to a ground station, wherein the ground station is coupled tothe shared ground power unit; and an aerial vehicle coupled to thetether, wherein the aerial vehicle is configured to operate in crosswindflight to generate electrical power.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts an Airborne Wind Turbine (AWT), according to an exampleembodiment.

FIG. 2 is a simplified block diagram illustrating components of an AWT,according to an example embodiment.

FIGS. 3A and 3B depict an example of an aerial vehicle transitioningfrom hover flight to crosswind flight, according to an exampleembodiment.

FIG. 3C depicts an example of an aerial vehicle transitioning from hoverflight to crosswind flight in a tether sphere, according to an exampleembodiment.

FIGS. 4A and 4B depict an aerial vehicle generating power, according toan example embodiment.

FIG. 5 is a simplified block diagram illustrating a system, according toan exemplary embodiment.

FIGS. 6A and 6B are flowcharts of methods, according to exemplaryembodiments.

FIGS. 7A and 7B are power profiles of aerial vehicles, according to anexemplary embodiment.

FIG. 8 illustrates an aerial vehicle deployed into hover flight,according to an exemplary embodiment.

FIG. 9 is a flowchart of a method, according to exemplary embodiment.

FIG. 10 is a flowchart of a method, according to an example embodiment.

FIGS. 11A and 11B depict aerial vehicles operating according todetermined flight settings, according to an example embodiment.

DETAILED DESCRIPTION

Exemplary methods and systems are described herein. It should beunderstood that the word “exemplary” is used herein to mean “serving asan example, instance, or illustration.” Any embodiment or featuredescribed herein as “exemplary” or “illustrative” is not necessarily tobe construed as preferred or advantageous over other embodiments orfeatures. More generally, the embodiments described herein are not meantto be limiting. It will be readily understood that certain aspects ofthe disclosed methods systems and can be arranged and combined in a widevariety of different configurations, all of which are contemplatedherein.

I. Overview

Illustrative embodiments relate to aerial vehicles, which may be used ina wind energy system, such as an Airborne Wind Turbine (AWT). Inparticular, illustrative embodiments may relate to or take the form ofmethods and systems for transitioning aerial vehicles between certainflight modes that facilitate conversion of kinetic energy to electricalenergy.

By way of background, an AWT may include an aerial vehicle that flies ina path, such as a substantially circular path, to convert kinetic windenergy to electrical energy. In an illustrative implementation, theaerial vehicle may be connected to a ground station via a tether. Whiletethered, the aerial vehicle can: (i) fly at a range of elevations andsubstantially along the path, and return to the ground, and (ii)transmit electrical energy to the ground station via the tether. (Insome embodiments, the ground station may transmit electricity to theaerial vehicle for take-off and/or landing.)

In an AWT, an aerial vehicle may rest in and/or on a ground station (orperch) when the wind is not conducive to power generation. When the windis conducive to power generation, such as when a wind speed may be 3.5meters per second (m/s) at an altitude of 200 meters (m), the groundstation may deploy (or launch) the aerial vehicle. In addition, when theaerial vehicle is deployed and the wind is not conducive to powergeneration, the aerial vehicle may return to the ground station.

Moreover, in an AWT, an aerial vehicle may be configured for crosswindflight. Crosswind flight may be used to travel in a motion, such as asubstantially circular motion, and thus may be the primary techniquethat is used to generate electrical energy. In crosswind flight, theaerial vehicle may be propelled by the wind substantially along a pathto convert kinetic wind energy to electrical energy. In someembodiments, the one or more propellers of the aerial vehicle maygenerate electrical energy by slowing down the incident wind.

In an embodiment of a wind energy system, a ground station of an AWT maybe connected to a ground power unit, which may connect the groundstation to an electric power grid using grid connections. In thisarrangement, the power generated by an aerial vehicle of the AWT mayflow, via a tether, from the aerial vehicle to the ground station. Thegenerated power may then flow from the ground station to the groundpower unit, where it may be transmitted to the electrical grid.

Within examples, more than one AWT may be connected to a shared groundpower unit, to decrease infrastructure costs for instance. Generally,the cost of electrical components, which are typically sized to handlethe peak power that may flow through the system, increases as thecomponents' power rating increases. As such, connecting more than oneAWT to a shared ground power unit may increase the cost of at least thegrid connections in the ground power unit, as the peak power that mayflow through the system may increase as the number of aerial vehiclesconnected to the shared ground station increases.

For example, the peak power that may flow through the system mayincrease when a plurality of aerial vehicles are deployed at the sametime. Additionally, if multiple AWTs sharing a ground power unit areflown in a synchronous or near-synchronous pattern, the peak powertransmission from each AWT may coincide in time, and thus may result ina very large peak power handling requirement of the ground power unit.

Consequently, the cumulative instantaneous power flow, into the sharedground power unit, may fluctuate due to power of differentcharacteristics (from each of the aerial vehicles) aggregating to formthe cumulative power flow. Therefore, the power received at the groundpower unit may be aperiodic, irregular, and may ripple, which may resultin the electrical grid receiving a fluctuating power input from theshared ground power unit.

Accordingly, each of the aerial vehicles connected to a shared groundpower unit may be deployed asynchronously. In asynchronous deployment, afirst aerial vehicle may be deployed. However, rather than enteringcrosswind flight, the first aerial vehicle may enter loitering flight,where the aerial vehicle may generate as much energy as it is usingresulting in zero or near-zero load on the shared ground power unit.While the first aerial vehicle is in loitering flight, each additionalaerial vehicle connected to the shared ground power unit mayasynchronously launch and enter loitering flight, until all of theaerial vehicles connected to a shared ground power unit have launched.Note that the last aerial vehicle may be deployed directly intocrosswind flight. Thus, by staggering the deployment of the aerialvehicles, the peak power that may flow through the system may be limitedto the peak power required to launch a single aerial vehicle.

Further, after the last aerial vehicle has transitioned into crosswindflight, the other aerial vehicles may also transition to crosswindflight. While in crosswind flight, the aerial vehicles may be operableto fly in a determined asynchronous pattern. More specifically, theflight path of each deployed aerial vehicle may be determined such thatthe phase of the power profile of each aerial vehicle may be out ofphase with respect to the power profile of each of the other aerialvehicles. As such, the overall peak power in the system may be decreasedas the aerial vehicles fly in a determined asynchronous pattern. Thepeak power in the system may be decreased by determining the flight pathof each aerial vehicle such that the peak power generated by each aerialvehicle may be out of phase with respect to the peak power generated bythe other aerial vehicles. Further, the aerial vehicles flying in adetermined asynchronous pattern may achieve a substantially regularpower flow. The aerial vehicles, which may be flying in a determinedasynchronous pattern, may be described as flying “in-sync”.

In line with the discussion above, the aerial vehicles may generateelectrical energy in crosswind flight and may thereby allow the AWTs toextract useful power from the wind. The aerial vehicles may generateelectrical energy during various environmental conditions such as highwind speeds, large gusts, turbulent air, or variable wind conditions.However, at times, the environmental conditions may cause one or more ofthe aerial vehicles to deviate from its determined flight patternrelative to the other vehicles flying in the determined asynchronouspattern. The aerial vehicle which deviates from its determined flightpattern may be referred to as an “out-of-sync” aerial vehicle relativeto the aerial vehicles flying in the determined flight pattern. As aresult, the power profile of each of the one or more out-of-sync aerialvehicles may no longer be out of phase with respect to the power profileof each of the other aerial vehicles. Therefore, the peak power that mayflow through the system may exceed the rated power of the electricalcomponents. Further, the cumulative power input into the electrical gridmay fluctuate.

Accordingly, at least the one or more out of sync aerial vehicles mayadjust one or more of their flight settings to resynchronize with theaerial vehicles flying in the determined asynchronous pattern.Alternatively, the control system of each of the aerial vehiclesconnected to the shared ground power unit may adjust one or more oftheir flight settings such that the aerial vehicles fly in an adjustedasynchronous pattern. Thus, the power profile of each of the aerialvehicles flying in the adjusted asynchronous pattern may be out of phasewith respect to the power profiles of each of the other aerial vehicles.

II. Illustrative Systems A. Airborne Wind Turbine (AWT)

FIG. 1 depicts an AWT 100, according to an example embodiment. Inparticular, the AWT 100 includes a ground station 110, a tether 120, andan aerial vehicle 130. As shown in FIG. 1, the aerial vehicle 130 may beconnected to the tether 120, and the tether 120 may be connected to theground station 110. In this example, the tether 120 may be attached tothe ground station 110 at one location on the ground station 110, andattached to the aerial vehicle 130 at two locations on the aerialvehicle 130. However, in other examples, the tether 120 may be attachedat multiple locations to any part of the ground station 110 and/or theaerial vehicle 130.

The ground station 110 may be used to hold and/or support the aerialvehicle 130 until it is in an operational mode. The ground station 110may also be configured to allow for the repositioning of the aerialvehicle 130 such that deploying of the device is possible. Further, theground station 110 may be further configured to receive the aerialvehicle 130 during a landing. The ground station 110 may be formed ofany material that can suitably keep the aerial vehicle 130 attachedand/or anchored to the ground while in hover flight, forward flight,crosswind flight.

In addition, the ground station 110 may include one or more components(not shown), such as a winch, that may vary a length of the tether 120.For example, when the aerial vehicle 130 is deployed, the one or morecomponents may be configured to pay out and/or reel out the tether 120.In some implementations, the one or more components may be configured topay out and/or reel out the tether 120 to a predetermined length. Asexamples, the predetermined length could be equal to or less than amaximum length of the tether 120. Further, when the aerial vehicle 130lands in the ground station 110, the one or more components may beconfigured to reel in the tether 120.

The tether 120 may transmit electrical energy generated by the aerialvehicle 130 to the ground station 110. In addition, the tether 120 maytransmit electricity to the aerial vehicle 130 in order to power theaerial vehicle 130 for takeoff, landing, hover flight, and/or forwardflight. The tether 120 may be constructed in any form and using anymaterial which may allow for the transmission, delivery, and/orharnessing of electrical energy generated by the aerial vehicle 130and/or transmission of electricity to the aerial vehicle 130. The tether120 may also be configured to withstand one or more forces of the aerialvehicle 130 when the aerial vehicle 130 is in an operational mode. Forexample, the tether 120 may include a core configured to withstand oneor more forces of the aerial vehicle 130 when the aerial vehicle 130 isin hover flight, forward flight, and/or crosswind flight. The core maybe constructed of any high strength fibers. In some examples, the tether120 may have a fixed length and/or a variable length. For instance, inat least one such example, the tether 120 may have a length of 140meters.

The aerial vehicle 130 may be configured to fly substantially along apath 150 to generate electrical energy. The term “substantially along,”as used in this disclosure, refers to exactly along and/or one or moredeviations from exactly along that do not significantly impactgeneration of electrical energy as described herein and/or transitioningan aerial vehicle between certain flight modes as described herein.

The aerial vehicle 130 may include or take the form of various types ofdevices, such as a kite, a helicopter, a wing and/or an airplane, amongother possibilities. The aerial vehicle 130 may be formed of solidstructures of metal, plastic and/or other polymers. The aerial vehicle130 may be formed of any material which allows for a highthrust-to-weight ratio and generation of electrical energy which may beused in utility applications. Additionally, the materials may be chosento allow for a lightning hardened, redundant and/or fault tolerantdesign which may be capable of handling large and/or sudden shifts inwind speed and wind direction. Other materials may be possible as well.

The path 150 may be various different shapes in various differentembodiments. For example, the path 150 may be substantially circular.And in at least one such example, the path 150 may have a radius of upto 265 meters. The term “substantially circular,” as used in thisdisclosure, refers to exactly circular and/or one or more deviationsfrom exactly circular that do not significantly impact generation ofelectrical energy as described herein. Other shapes for the path 150 maybe an oval, such as an ellipse, the shape of a jelly bean, the shape ofthe number of 8, etc.

As shown in FIG. 1, the aerial vehicle 130 may include a main wing 131,a front section 132, rotor connectors 133A-B, rotors 134A-D, a tail boom135, a tail wing 136, and a vertical stabilizer 137. Any of thesecomponents may be shaped in any form which allows for the use ofcomponents of lift to resist gravity and/or move the aerial vehicle 130forward.

The main wing 131 may provide a primary lift for the aerial vehicle 130.The main wing 131 may be one or more rigid or flexible airfoils, and mayinclude various control surfaces, such as winglets, flaps, rudders,elevators, etc. The control surfaces may be used to stabilize the aerialvehicle 130 and/or reduce drag on the aerial vehicle 130 during hoverflight, forward flight, and/or crosswind flight.

The main wing 131 may be any suitable material for the aerial vehicle130 to engage in hover flight, forward flight, and/or crosswind flight.For example, the main wing 131 may include carbon fiber and/or e-glass.Moreover, the main wing 131 may have a variety dimensions. For example,the main wing 131 may have one or more dimensions that correspond with aconventional wind turbine blade. As another example, the main wing 131may have a span of 8 meters, an area of 4 meters squared, and an aspectratio of 15. The front section 132 may include one or more components,such as a nose, to reduce drag on the aerial vehicle 130 during flight.

The rotor connectors 133A-B may connect the rotors 134A-D to the mainwing 131. In some examples, the rotor connectors 133A-B may take theform of or be similar in form to one or more pylons. In this example,the rotor connectors 133A-B are arranged such that the rotors 134A-D arespaced between the main wing 131. In some examples, a vertical spacingbetween corresponding rotors (e.g., rotor 134A and rotor 134B or rotor134C and rotor 134D) may be 0.9 meters.

The rotors 134A-D may be configured to drive one or more generators forthe purpose of generating electrical energy. In this example, the rotors134A-D may each include one or more blades, such as three blades. Theone or more rotor blades may rotate via interactions with the wind andwhich could be used to drive the one or more generators. In addition,the rotors 134A-D may also be configured to provide a thrust to theaerial vehicle 130 during flight. With this arrangement, the rotors134A-D may function as one or more propulsion units, such as apropeller. Although the rotors 134A-D are depicted as four rotors inthis example, in other examples the aerial vehicle 130 may include anynumber of rotors, such as less than four rotors or more than fourrotors.

The tail boom 135 may connect the main wing 131 to the tail wing 136.The tail boom 135 may have a variety of dimensions. For example, thetail boom 135 may have a length of 2 meters. Moreover, in someimplementations, the tail boom 135 could take the form of a body and/orfuselage of the aerial vehicle 130. And in such implementations, thetail boom 135 may carry a payload.

The tail wing 136 and/or the vertical stabilizer 137 may be used tostabilize the aerial vehicle and/or reduce drag on the aerial vehicle130 during hover flight, forward flight, and/or crosswind flight. Forexample, the tail wing 136 and/or the vertical stabilizer 137 may beused to maintain a pitch of the aerial vehicle 130 during hover flight,forward flight, and/or crosswind flight. In this example, the verticalstabilizer 137 is attached to the tail boom 135, and the tail wing 136is located on top of the vertical stabilizer 137. The tail wing 136 mayhave a variety of dimensions. For example, the tail wing 136 may have alength of 2 meters. Moreover, in some examples, the tail wing 136 mayhave a surface area of 0.45 meters squared. Further, in some examples,the tail wing 136 may be located 1 meter above a center of mass of theaerial vehicle 130.

While the aerial vehicle 130 has been described above, it should beunderstood that the methods and systems described herein could involveany suitable aerial vehicle that is connected to a tether, such as thetether 120.

B. Illustrative Components of an AWT

FIG. 2 is a simplified block diagram illustrating components of the AWT200. The AWT 200 may take the form of or be similar in form to the AWT100. In particular, the AWT 200 includes a ground station 210, a tether220, and an aerial vehicle 230. The ground station 210 may take the formof or be similar in form to the ground station 110, the tether 220 maytake the form of or be similar in form to the tether 120, and the aerialvehicle 230 may take the form of or be similar in form to the aerialvehicle 130.

As shown in FIG. 2, the ground station 210 may include one or moreprocessors 212, data storage 214, and program instructions 216. Aprocessor 212 may be a general-purpose processor or a special purposeprocessor (e.g., digital signal processors, application specificintegrated circuits, etc.). The one or more processors 212 can beconfigured to execute computer-readable program instructions 216 thatare stored in data storage 214 and are executable to provide at leastpart of the functionality described herein.

The data storage 214 may include or take the form of one or morecomputer-readable storage media that may be read or accessed by at leastone processor 212. The one or more computer-readable storage media caninclude volatile and/or non-volatile storage components, such asoptical, magnetic, organic or other memory or disc storage, which may beintegrated in whole or in part with at least one of the one or moreprocessors 212. In some embodiments, the data storage 214 may beimplemented using a single physical device (e.g., one optical, magnetic,organic or other memory or disc storage unit), while in otherembodiments, the data storage 214 can be implemented using two or morephysical devices.

As noted, the data storage 214 may include computer-readable programinstructions 216 and perhaps additional data, such as diagnostic data ofthe ground station 210. As such, the data storage 214 may includeprogram instructions to perform or facilitate some or all of thefunctionality described herein.

In a further respect, the ground station 210 may include a communicationsystem 218. The communications system 218 may include one or morewireless interfaces and/or one or more wireline interfaces, which allowthe ground station 210 to communicate via one or more networks. Suchwireless interfaces may provide for communication under one or morewireless communication protocols, such as Bluetooth, WiFi (e.g., an IEEE802.11 protocol), Long-Term Evolution (LTE), WiMAX (e.g., an IEEE 802.16standard), a radio-frequency ID (RFID) protocol, near-fieldcommunication (NFC), and/or other wireless communication protocols. Suchwireline interfaces may include an Ethernet interface, a UniversalSerial Bus (USB) interface, or similar interface to communicate via awire, a twisted pair of wires, a coaxial cable, an optical link, afiber-optic link, or other physical connection to a wireline network.The ground station 210 may communicate with the aerial vehicle 230,other ground stations, and/or other entities (e.g., a command center)via the communication system 218.

In an example embodiment, the ground station 210 may includecommunication systems 218 that allows for both short-range communicationand long-range communication. For example, the ground station 210 may beconfigured for short-range communications using Bluetooth and forlong-range communications under a CDMA protocol. In such an embodiment,the ground station 210 may be configured to function as a “hot spot”; orin other words, as a gateway or proxy between a remote support device(e.g., the tether 220, the aerial vehicle 230, and other groundstations) and one or more data networks, such as cellular network and/orthe Internet. Configured as such, the ground station 210 may facilitatedata communications that the remote support device would otherwise beunable to perform by itself.

For example, the ground station 210 may provide a WiFi connection to theremote device, and serve as a proxy or gateway to a cellular serviceprovider's data network, which the ground station 210 might connect tounder an LTE or a 3G protocol, for instance. The ground station 210could also serve as a proxy or gateway to other ground stations or acommand station, which the remote device might not be able to otherwiseaccess.

Moreover, as shown in FIG. 2, the tether 220 may include transmissioncomponents 222 and a communication link 224. The transmission components222 may be configured to transmit electrical energy from the aerialvehicle 230 to the ground station 210 and/or transmit electrical energyfrom the ground station 210 to the aerial vehicle 230. The transmissioncomponents 222 may take various different forms in various differentembodiments. For example, the transmission components 222 may includeone or more conductors that are configured to transmit electricity. Andin at least one such example, the one or more conductors may includealuminum and/or any other material which allows for the conduction ofelectric current. Moreover, in some implementations, the transmissioncomponents 222 may surround a core of the tether 220 (not shown).

The ground station 210 could communicate with the aerial vehicle 230 viathe communication link 224. The communication link 224 may bebidirectional and may include one or more wired and/or wirelessinterfaces. Also, there could be one or more routers, switches, and/orother devices or networks making up at least a part of the communicationlink 224.

Further, as shown in FIG. 2, the aerial vehicle 230 may include one ormore sensors 232, a power system 234, power generation/conversioncomponents 236, a communication system 238, one or more processors 242,data storage 244, and program instructions 246, and a control system248.

The sensors 232 could include various different sensors in variousdifferent embodiments. For example, the sensors 232 may include a globala global positioning system (GPS) receiver. The GPS receiver may beconfigured to provide data that is typical of well-known GPS systems(which may be referred to as a global navigation satellite system(GNNS)), such as the GPS coordinates of the aerial vehicle 230. Such GPSdata may be utilized by the AWT 200 to provide various functionsdescribed herein.

As another example, the sensors 232 may include one or more windsensors, such as one or more pitot tubes. The one or more wind sensorsmay be configured to detect apparent and/or relative wind. Theapparent/relative wind may be wind that is being applied to the aerialvehicle 230, for example. Such wind data may be utilized by the AWT 200to provide various functions described herein.

Still as another example, the sensors 232 may include an inertialmeasurement unit (IMU). The IMU may include both an accelerometer and agyroscope, which may be used together to determine the orientation ofthe aerial vehicle 230. In particular, the accelerometer can measure theorientation of the aerial vehicle 230 with respect to earth, while thegyroscope measures the rate of rotation around an axis, such as acenterline of the aerial vehicle 230. IMUs are commercially available inlow-cost, low-power packages. For instance, the IMU may take the form ofor include a miniaturized MicroElectroMechanical System (MEMS) or aNanoElectroMechanical System (NEMS). Other types of IMUs may also beutilized. The IMU may include other sensors, in addition toaccelerometers and gyroscopes, which may help to better determineposition. Two examples of such sensors are magnetometers and pressuresensors. Other examples of sensors are also possible.

While an accelerometer and gyroscope may be effective at determining theorientation of the aerial vehicle 230, slight errors in measurement maycompound over time and result in a more significant error. However, anexample aerial vehicle 230 may be able mitigate or reduce such errors byusing a magnetometer to measure direction. One example of a magnetometeris a low-power, digital 3-axis magnetometer, which may be used torealize an orientation independent electronic compass for accurateheading information. However, other types of magnetometers may beutilized as well.

The aerial vehicle 230 may also include a pressure sensor or barometer,which can be used to determine the altitude of the aerial vehicle 230.Alternatively, other sensors, such as sonic altimeters or radaraltimeters, can be used to provide an indication of altitude, which mayhelp to improve the accuracy of and/or prevent drift of the IMU.

As noted, the aerial vehicle 230 may include the power system 234. Thepower system 234 could take various different forms in various differentembodiments. For example, the power system 234 may include one or morebatteries for providing power to the aerial vehicle 230. In someimplementations, the one or more batteries may be rechargeable and eachbattery may be recharged via a wired connection between the battery anda power supply and/or via a wireless charging system, such as aninductive charging system that applies an external time-varying magneticfield to an internal battery and/or charging system that uses energycollected from one or more solar panels.

As another example, the power system 234 may include one or more motorsor engines for providing power to the aerial vehicle 230. In someimplementations, the one or more motors or engines may be powered by afuel, such as a hydrocarbon-based fuel. And in such implementations, thefuel could be stored on the aerial vehicle 230 and delivered to the oneor more motors or engines via one or more fluid conduits, such aspiping. In some implementations, the power system 234 may be implementedin whole or in part on the ground station 210.

As noted, the aerial vehicle 230 may include the powergeneration/conversion components 236. The power generation/conversioncomponents 326 could take various different forms in various differentembodiments. For example, the power generation/conversion components 236may include one or more generators, such as high-speed, direct-drivegenerators. With this arrangement, the one or more generators may bedriven by one or more rotors, such as the rotors 134A-D. And in at leastone such example, the one or more generators may operate at full ratedpower wind speeds of 11.5 meters per second at a capacity factor whichmay exceed 60 percent, and the one or more generators may generateelectrical power from 40 kilowatts to 600 megawatts.

Moreover, as noted, the aerial vehicle 230 may include a communicationsystem 238. The communication system 238 may take the form of or besimilar in form to the communication system 218. The aerial vehicle 230may communicate with the ground station 210, other aerial vehicles,and/or other entities (e.g., a command center) via the communicationsystem 238.

In some implementations, the aerial vehicle 230 may be configured tofunction as a “hot spot”; or in other words, as a gateway or proxybetween a remote support device (e.g., the ground station 210, thetether 220, other aerial vehicles) and one or more data networks, suchas cellular network and/or the Internet. Configured as such, the aerialvehicle 230 may facilitate data communications that the remote supportdevice would otherwise be unable to perform by itself.

For example, the aerial vehicle 230 may provide a WiFi connection to theremote device, and serve as a proxy or gateway to a cellular serviceprovider's data network, which the aerial vehicle 230 might connect tounder an LTE or a 3G protocol, for instance. The aerial vehicle 230could also serve as a proxy or gateway to other aerial vehicles or acommand station, which the remote device might not be able to otherwiseaccess.

As noted, the aerial vehicle 230 may include the one or more processors242, the program instructions 244, and the data storage 246. The one ormore processors 242 can be configured to execute computer-readableprogram instructions 246 that are stored in the data storage 244 and areexecutable to provide at least part of the functionality describedherein. The one or more processors 242 may take the form of or besimilar in form to the one or more processors 212, the data storage 244may take the form of or be similar in form to the data storage 214, andthe program instructions 246 may take the form of or be similar in formto the program instructions 216.

Moreover, as noted, the aerial vehicle 230 may include the controlsystem 248. In some implementations, the control system 248 may beconfigured to perform one or more functions described herein. Thecontrol system 248 may be implemented with mechanical systems and/orwith hardware, firmware, and/or software. As one example, the controlsystem 248 may take the form of program instructions stored on anon-transitory computer readable medium and a processor that executesthe instructions. The control system 248 may be implemented in whole orin part on the aerial vehicle 230 and/or at least one entity remotelylocated from the aerial vehicle 230, such as the ground station 210.Generally, the manner in which the control system 248 is implemented mayvary, depending upon the particular application.

While the aerial vehicle 230 has been described above, it should beunderstood that the methods and systems described herein could involveany suitable aerial vehicle that is connected to a tether, such as thetether 230 and/or the tether 110.

C. Transitioning an Aerial Vehicle from Hover Flight to Crosswind Flightto Generate Power

FIGS. 3A and 3B depict an example 300 of transitioning an aerial vehiclefrom hover flight to crosswind flight in a manner such that power may begenerated, according to an example embodiment. Example 300 is generallydescribed by way of example as being carried out by the aerial vehicle130 described above in connection with FIG. 1. For illustrativepurposes, example 300 is described in a series of actions as shown inFIGS. 3A and 3B, though example 300 could be carried out in any numberof actions and/or combination of actions.

As shown in FIG. 3A, the aerial vehicle 130 may be connected to thetether 120, and the tether 120 is connected to the ground station 110.The ground station 110 is located on ground 302. Moreover, as shown inFIG. 3A, the tether 120 defines a tether sphere 304 having a radiusbased on a length of the tether 120, such as a length of the tether 120when it is extended. Example 300 may be carried out in and/orsubstantially on a portion 304A of the tether sphere 304. The term“substantially on,” as used in this disclosure, refers to exactly onand/or one or more deviations from exactly on that do not significantlyimpact transitioning an aerial vehicle between certain flight modes asdescribed herein.

Example 300 begins at a point 306 with deploying the aerial vehicle 130from the ground station 110 in a hover-flight orientation. With thisarrangement, the tether 120 may be paid out and/or reeled out. In someimplementations, the aerial vehicle 130 may be deployed when wind speedsincrease above a threshold speed (e.g., 3.5 m/s) at a threshold altitude(e.g., over 200 meters above the ground 302).

Further, at point 306 the aerial vehicle 130 may be operated in thehover-flight orientation. When the aerial vehicle 130 is in thehover-flight orientation, the aerial vehicle 130 may engage in hoverflight. For instance, when the aerial vehicle engages in hover flight,the aerial vehicle 130 may ascend, descend, and/or hover over the ground302. When the aerial vehicle 130 is in the hover-flight orientation, aspan of the main wing 131 of the aerial vehicle 130 may be orientedsubstantially perpendicular to the ground 302. The term “substantiallyperpendicular,” as used in this disclosure, refers to exactlyperpendicular and/or one or more deviations from exactly perpendicularthat do not significantly impact transitioning an aerial vehicle betweencertain flight modes as described herein.

Example 300 continues at a point 308 with while the aerial vehicle 130is in the hover-flight orientation positioning the aerial vehicle 130 ata first location 310 that is substantially on the tether sphere 304. Asshown in FIG. 3A, the first location 310 may be in the air andsubstantially downwind of the ground station 110.

The term “substantially downwind,” as used in this disclosure, refers toexactly downwind and/or one or more deviations from exactly downwindthat do not significantly impact transitioning an aerial vehicle betweencertain flight modes as described herein.

For example, the first location 310 may be at a first angle from an axisextending from the ground station 110 that is substantially parallel tothe ground 302. In some implementations, the first angle may be 30degrees from the axis. In some situations, the first angle may bereferred to as azimuth, and the first angle may be between 30 degreesclockwise from the axis and 330 degrees clockwise from the axis, such as15 degrees clockwise from the axis or 345 degrees clockwise from theaxis.

As another example, the first location 310 may be at a second angle fromthe axis. In some implementations, the second angle may be 10 degreesfrom the axis. In some situations, the second angle may be referred toas elevation, and the second angle may be between 10 degrees in adirection above the axis and 10 degrees in a direction below the axis.The term “substantially parallel,” as used in this disclosure refers toexactly parallel and/or one or more deviations from exactly parallelthat do not significantly impact transitioning an aerial vehicle betweencertain flight modes described herein.

At point 308, the aerial vehicle 130 may accelerate in the hover-flightorientation. For example, at point 308, the aerial vehicle 130 mayaccelerate up to a few meters per second. In addition, at point 308, thetether 120 may take various different forms in various differentembodiments. For example, as shown in FIG. 3A, at point 308 the tether120 may be extended. With this arrangement, the tether 120 may be in acatenary configuration. Moreover, at point 306 and point 308, a bottomof the tether 120 may be a predetermined altitude 312 above the ground302. With this arrangement, at point 306 and point 308 the tether 120may not contact the ground 302.

Example 300 continues at point 314 with transitioning the aerial vehicle130 from the hover-flight orientation to a forward-flight orientation,such that the aerial vehicle 130 moves from the tether sphere 304. Asshown in FIG. 3B, the aerial vehicle 130 may move from the tether sphere304 to a location toward the ground station 110 (which may be referredto as being inside the tether sphere 304).

When the aerial vehicle 130 is in the forward-flight orientation, theaerial vehicle 130 may engage in forward flight (which may be referredto as airplane-like flight). For instance, when the aerial vehicle 130engages in forward flight, the aerial vehicle 130 may ascend. Theforward-flight orientation of the aerial vehicle 130 could take the formof an orientation of a fixed-wing aircraft (e.g., an airplane) inhorizontal flight. In some examples, transitioning the aerial vehicle130 from the hover-flight orientation to the forward-flight orientationmay involve a flight maneuver, such as pitching forward. And in such anexample, the flight maneuver may be executed within a time period, suchas less than one second.

At point 314, the aerial vehicle 130 may achieve attached flow. Further,at point 314, a tension of the tether 120 may be reduced. With thisarrangement, a curvature of the tether 120 at point 314 may be greaterthan a curvature of the tether 120 at point 308. As one example, atpoint 314, the tension of the tether 120 may be less than 1 KN, such as500 newtons (N).

Example 300 continues at one or more points 318 with operating theaerial vehicle 130 in the forward-flight orientation to ascend at anangle of ascent to a second location 320 that is substantially on thetether sphere 304. As shown in FIG. 3B, the aerial vehicle 130 may flysubstantially along a path 316 during the ascent at one or more points318. In this example, one or more points 318 is shown as three points, apoint 318A, a point 318B, and a point 318C. However, in other examples,one or more points 318 may include less than three or more than threepoints.

In some examples, the angle of ascent may be an angle between the path316 and the ground 302. Further, the path 316 may take various differentforms in various different embodiments. For instance, the path 316 maybe a line segment, such as a chord of the tether sphere 304.

As shown in FIG. 3B, the second location 320 may be in the air andsubstantially downwind of the ground station 110. The second location320 may be oriented with respect to the ground station 110 the similarway as the first location 310 may be oriented with respect to the groundstation 110.

For example, the second location 320 may be at a first angle from anaxis extending from the ground station 110 that is substantiallyparallel to the ground 302. In some implementations, the first angle maybe 30 degrees from the axis. In some situations, the first angle may bereferred to as azimuth, and the angle may be between 30 degreesclockwise from the axis and 330 degrees clockwise from the axis, such as15 degrees clockwise from the axis or 345 degrees clockwise from theaxis.

In addition, as shown in FIG. 3B, the second location 320 may besubstantially upwind of the first location 310. The term “substantiallyupwind,” as used in this disclosure, refers to exactly upwind and/or oneor more deviations from exactly upwind that do not significantly impacttransitioning an aerial vehicle between certain flight modes asdescribed herein.

At one or more points 318, a tension of the tether 120 may increaseduring the ascent. For example, a tension of the tether 120 at point318C may be greater than a tension of the tether 120 at point 318B, atension of the tether 120 at point 318B may be greater than a tension ofthe tether 120 at point 318A. Further, a tension of the tether 120 atpoint 318A may be greater than a tension of the tether at point 314.

With this arrangement, a curvature of the tether 120 may decrease duringthe ascent. For example, a curvature the tether 120 at point 318C may beless than a curvature the tether at point 318B, and a curvature of thetether 120 at point 318B may be less than a curvature of the tether atpoint 318A. Further, in some examples, a curvature of the tether 120 atpoint 318A may be less than a curvature of the tether 120 at point 314.

Example 300 continues at a point 322 with transitioning the aerialvehicle 130 from the forward-flight orientation to a crosswind-flightorientation. In some examples, transitioning the aerial vehicle 130 fromthe forward-flight orientation to the crosswind-flight orientation mayinvolve a flight maneuver. When the aerial vehicle 130 is in thecrosswind-flight orientation, the aerial vehicle 130 may engage incrosswind flight. For instance, when the aerial vehicle 130 engages incrosswind flight, the aerial vehicle 130 may fly substantially along apath, such as path 150, to generate electrical energy. In someimplementations, a natural roll and/or yaw of the aerial vehicle 130 mayoccur during crosswind flight.

FIG. 3C depicts example 300 from a three-dimensional (3D) perspective.Accordingly, like numerals may denote like entities. As noted above,tether sphere 304 has a radius based on a length of a tether 120, suchas a length of the tether 120 when it is extended. Also as noted above,in FIG. 3C, the tether 120 is connected to ground station 310, and theground station 310 is located on ground 302. Further, relative wind 303contacts the tether sphere 304. Note, in FIG. 3C, only a portion of thetether sphere 304 that is above the ground 302 is depicted. The portionmay be described as one half of the tether sphere 304.

As shown in FIG. 3C, the first portion 304A of the tether sphere 304 issubstantially downwind of the ground station 310. In FIG. 3C, the firstportion 304A may be described as one quarter of the tether sphere 304.

Like FIG. 3B, FIG. 3C depicts transitioning aerial vehicle 130 (notshown in FIG. 3C to simply the Figure) between hover flight andcrosswind flight. As shown in FIG. 3C, when the aerial vehicle 130transitions from the hover-flight orientation to a forward-flightorientation, the aerial vehicle may be positioned at a point 314 that isinside the first portion 304A of the tether sphere 304. Further still,as shown in FIG. 3C, when aerial vehicle 130 ascends in theforward-flight orientation to a location 320 that is substantially onthe first portion 304A of the tether sphere 304, the aerial vehicle mayfollow a path 316. Yet even further, as shown in FIG. 3C, aerial vehicle130 may then transition from location 320 in a forward-flightorientation to a crosswind flight orientation at location 322, forexample.

Illustrative embodiments relate to aerial vehicles, which may be used ina wind energy system, such as an Airborne Wind Turbine (AWT). Inparticular, illustrative embodiments may relate to or take the form ofmethods and systems for transitioning an aerial vehicle between certainflight modes that facilitate conversion of kinetic energy to electricalpower.

D. Power Generation in Crosswind Flight

As explained above, the aerial vehicle 130 may fly substantially along aflight path, while operating in crosswind flight, to generate electricalpower. The instantaneous electrical power generated by the aerialvehicle 130 may depend on the location of the aerial vehicle 130 in itsflight path. Therefore, the instantaneous power generated by the aerialvehicle 130 may oscillate as the aerial vehicle 130 circulates itsflight path. Further, the instantaneous generated power may also beperiodic as the aerial vehicle 130 may repeatedly circulate its flightpath. Each full circulation of the flight path may correspond to aperiod, T, of the periodically oscillating generated power. Therefore,the characteristics of the generated power, such as the frequency, maydepend on the aerial vehicle 130's flight path.

For example, a profile of the power generated by the aerial vehicle 130as a function of time (also referred to herein as a “power profile”) mayvary approximately sinusoidally as the aerial vehicle 130 circulates itsflight path. FIG. 4A illustrates an aerial vehicle, which may generate asinusoidally varying power profile, according to an exemplaryembodiment. FIG. 4B illustrates a period, T, of a sinusoidallyoscillating power profile 402 of the aerial vehicle 130 circling theflight path in a direction 414.

The period T of the power profile 402 corresponds to a full circulationof the flight path 404 by the aerial vehicle 130. For instance, startingat position 406 of the flight path 404, the aerial vehicle 130 flying atthat position generates an electrical power output represented by pointP₄₀₆ of the power profile 402. As the aerial vehicle 130 flies along theflight path 404 to position 408, the power generated by the aerialvehicle 130 decreases. The minimum generated power, represented by pointP₄₀₈ of the power profile 402, may be generated as the aerial vehicle130 flies at its highest position 408 (i.e. top of its flight path 404).As the aerial vehicle 130 continues to fly along the flight path 404 toreach the position 412 (i.e. the bottom of its flight path 404), thegenerated power increases. The peak generated power, represented bypoint P₄₁₂ of the power profile 402, may be generated as the aerialvehicle 130 flies at its lowest position 412.

The example provided in FIG. 4 and the accompanying description hereinis for illustrative purposes only and should not be considered limiting.For example, the power profile 402 may not be sinusoidal, but may varyin other approximately periodic fashions. As another example, all pointsalong the power profile 402 may not always reflect generated power, butrather certain segments of the flight path 404 may result in zero ornegative power generation, i.e., glide or power consumption, in whichpower may be supplied to the aerial vehicle in order to maintain itsflight path 404. As another example, the points of minimum P₄₀₈ andmaximum P₄₁₂ power generation may not correspond to the peak 408 andtrough 412 of the flight path 404, but may occur at some intermediatepositions along the flight path 404. Further, the flight path 404 maynot be circular as illustrated, but may be some other orbital path,including oblong, variable, and/or asymmetric orbital paths.

E. Ground Power Unit

In an implementation of a power generating system, the AWT 100 may becoupled, via the ground station 110, to a ground power unit. The groundpower unit may connect the ground station 110 to an electricaldistribution and transmission network (e.g., an electrical grid) viagrid connections. The grid connections may include electrical componentssuch as conductors (e.g. transmission lines), regulators, converters,inverters, transformers, rectifiers, capacitor banks, switches, andcircuit breakers. Furthermore, in such an implementation, the electricalpower generated by the aerial vehicle 130 may flow, via the tether 120,from the aerial vehicle 130 to the ground station 110. The generatedpower may then flow from the ground station 110 to the ground powerunit, where it may be transmitted to the electrical grid. The groundpower unit may also supply power, either from the electrical grid orfrom a back-up battery system, to the ground station 110 connected toit.

Within examples, the back-up battery system may be a component of theground power unit. The back-up battery system may include more than onebattery, connected in a parallel and/or series configuration, withsimilar or different batteries or circuits. Within examples, the batterysystem may include rechargeable batteries, which may be any one oflithium-ion batteries, lead-acid batteries, flow batteries,nickel-cadmium batteries, or any other type of rechargeable battery.

In some examples, the batteries may be recharged using power receivedfrom the electrical grid. In other examples, the batteries may berecharged using power generated by the aerial vehicle 130. Further, theback-up battery system may transmit electrical power to the electricalgrid, when the aerial vehicle 130 is not generating enough electricalpower, to maintain a constant flow of power to the electrical grid.

The battery system may also provide electrical power to the aerialvehicle 130. For instance, the electrical grid may be down and may beunable to provide the aerial vehicle 130 with electrical power, or itmay be more cost-effective to provide the aerial vehicle 130 with powerfrom the battery system than from the electrical grid. In an example,the aerial vehicle 130 may need electrical power to deploy, to land, tomaintain its flight path, and/or for an emergency situation. Thus, atleast in the situation where the electrical grid is incapable ofsupplying the aerial vehicle 130 with electrical power (e.g. theelectrical grid is down), the back-up battery system may supply theaerial vehicle 130 with the electrical power that it may require tooperate.

In some implementations of a power generating system, more than one AWTmay be connected to a single ground power unit. Connecting more than oneAWT to a single ground power unit may decrease infrastructure costs.Additionally, connecting more than one AWT to a shared ground power unitmay further decrease costs by decreasing the number of back-up batterysystems that may be included in a power generating system. For instance,the number of back-up battery systems may be reduced since the sharedground power unit may include a shared back-up battery system that mayprovide power to each of the aerial vehicles connected to the sharedground power unit of the power generating system.

FIG. 5 illustrates a system 500 that includes a plurality of AWTs,according to an exemplary embodiment. Specifically, the system 500includes two AWTs, AWT 502 and AWT 508, coupled to a shared ground powerunit 514. The example provided in FIG. 5 and the accompanyingdescription herein is for illustrative purposes only and should not beconsidered limiting. For example, the system 500 may include more thantwo AWTs. As another example, the shared ground power unit 514 mayinclude more than one battery system 518. In yet another example, thebattery 518 may be an entity independent from the shared ground powerunit 514.

Each AWT in FIG. 5 is coupled to the shared ground power unit 514 via arespective ground station. In this system, each aerial vehicle generateselectrical power, which flows via respective tethers (not illustrated)to the ground station 506 and the ground station 512 respectively. Eachground station transmits the power it receives to the shared groundpower unit 514. The cumulative electrical power transmitted to theshared ground power unit 514 is substantially the summation of theelectrical power generated by each aerial vehicle. Note that some of theelectrical power generated by the aerial vehicles may be dissipated dueto inefficiencies and losses.

The cumulative electrical power may be transmitted from the ground powerunit 514 to the electrical grid via the grid connections 516. The gridconnections 516 are typically sized to handle the peak power that mayflow through the system 500. Generally, the cost of electricalcomponents increases as the components' power rating increases. As such,connecting AWTs 502 and 508 to the shared ground power unit 514 mayincrease the peak power flowing through the ground power unit 514, asthe cumulative power flowing through the ground power unit 514 is thesummation of the powers received from AWTs 502 and 508. As a result, thecost of at least the grid connections 516 in the ground power unit 514may increase.

More specifically, as explained above, during crosswind flight, thepower profile of each aerial vehicle may be a periodically oscillatingprofile that may vary in phase, frequency, and amplitude depending onenvironmental and/or operating conditions. Consequently, the cumulativeinstantaneous power flow into the shared ground power unit 514 mayfluctuate due to power of different characteristics (from each of theaerial vehicles) aggregating to form the cumulative power flow. As aresult, the cumulative power profile received at the ground power unit514 may be aperiodic, irregular, and may ripple. Therefore, theelectrical grid may receive a fluctuating power input from the sharedground power unit 514.

For example, if the aerial vehicle 504 and the aerial vehicle 508 areflown in a synchronous or near-synchronous pattern, the peak powertransmission from each respective ground station may coincide in time,and thus may result in a very large peak power handling requirement ofthe ground power unit 514. However, in some embodiments, the aerialvehicle 504 and the aerial vehicle 508 may fly in an asynchronous flightpattern such that each aerial vehicle has a determined flight patternrelative to the other aerial vehicle. Accordingly, the asynchronousflight pattern may include a respective flight path for each aerialvehicle. The respective flight path may include the parameters of theflight path (i.e. location, perimeter, width, elevation, etc.) and thelocation of the each aerial vehicle relative to the other aerialvehicles as each aerial vehicle flies in its respective flight path.Accordingly, at a given time, each aerial vehicle may be a determinedlocation relative to the other aerial vehicle.

Further, the asynchronous flight pattern may be determined such that thepower profile of each aerial vehicle is out of phase with respect to thepower profile of the other aerial vehicle. As a result, the peakcumulative power flow into the ground power unit 514 may be decreased,and the cumulative power profile may be substantially regular.

Accordingly, FIG. 6A is a flowchart of an example process 600 foroperating two or more aerial vehicles according to an asynchronousflight pattern. Illustrative methods, such as method 600, may be carriedout in whole or in part by a component or components of each AWT, suchas by the one or more components of the aerial vehicle 230 shown in FIG.2 and the ground station 210 shown in FIG. 2. For example, method 600may be performed by the respective control system 248 of each aerialvehicle. However, it should be understood that example methods, such asmethod 600, may be carried out by other entities or combinations ofentities without departing from the scope of the disclosure.

As shown by block 602, method 600 involves determining an asynchronousflight pattern for two or more aerial vehicles. In an embodiment, theasynchronous flight pattern may include a respective flight path foreach of the aerial vehicles. Accordingly, the respective control systemof each aerial vehicle may determine the respective flight path for itsaerial vehicle. For example, the respective flight path of each aerialvehicle may be determined such that each aerial vehicle has a flightpattern relative to the other aerial vehicles operating according to theasynchronous pattern. In another example, the respective flight path ofeach aerial vehicle may be determined such that the phase of the powerprofile of the power generated by each aerial vehicle may be out ofphase with respect to the power profile of the power generated by theother aerial vehicles.

In some examples, the asynchronous flight pattern may be determined suchthat the cumulative power profile is substantially regular and/or thecumulative power output is greater than a certain threshold. Forinstance, the threshold may be the minimum output of power necessary forthe power generating system to be profitable. In other examples, theasynchronous flight pattern determination may be based on the respectivelocation of each aerial vehicle and/or the environmental conditionsapplicable to each aerial vehicle (i.e. the wind speed of the apparentwind-flow being applied to the respective aerial vehicle). Note that theexample considerations for determining the asynchronous flight patternare for example only and should not be considered limiting. For example,other considerations, such as those disclosed herein with respect tomethod 610, may be used in method 600.

Accordingly, in response to the asynchronous flight patterndetermination, the control system of each aerial vehicle may operateeach of the aerial vehicles in crosswind flight substantially along itsrespective flight path, as shown by block 604. The power profile of eachaerial vehicle may be out of phase with respect to each of the powerprofiles of the other aerial vehicles, as the aerial vehicles fly in thedetermined asynchronous flight pattern.

In another example, FIG. 6B is a flowchart of a process 610 foroperating two or more aerial vehicles according to an asynchronousflight pattern. In such a process, a respective preferred phase shiftbetween the power profiles of two of two or more aerial vehicles may bedetermined. The respective preferred phase shift between the powerprofiles of the two aerial vehicles may accordingly be used to determinean asynchronous flight pattern for the aerial vehicles. Morespecifically, the respective phase shift between the power profiles ofthe two aerial vehicles may be used to determine a respective flightpath for each of the two aerial vehicles.

As shown by block 612, method 610 involves determining at least onepreferred phase differential between the power profiles of two of theaerial vehicles. In some examples, the preferred phase differential maybe determined such that the cumulative power profile of the system hasspecific characteristics. For example, the preferred phase differentialmay be determined such that the cumulative power profile has a specificfrequency, duty cycle, and/or amplitude. Within examples, the preferredphase differential may be the same between the power profiles of any twoof the aerial vehicles.

Further, as shown by block 614, method 610 involves determining at leastan asynchronous flight pattern for the two or more aerial vehicles basedat least on the one preferred phase differential. Accordingly, thecontrol system of each aerial vehicle may determine the respectiveflight path of its aerial vehicle based on the at least one preferredphase differential. The control system of each aerial vehicle may useinformation such as the position of the other aerial vehicles, the windconditions, the determined preferred phase differential, and the powerdemand from the grid to determine the respective flight path for itsaerial vehicle. Further, as the respective flight path of each aerialvehicle is determined such that a preferred phase differential existsbetween any two of the aerial vehicles, the collective flight paths ofthe aerial vehicles consolidate to form the asynchronous flight patternfor the aerial vehicles. Note that the example considerations fordetermining the asynchronous flight pattern are for example only andshould not be considered limiting. For example, other considerations,such as those disclosed herein with respect to method 600, may be usedin method 610.

Finally, as shown by block 616, method 610 involves operating the aerialvehicles according to the determined asynchronous flight pattern.Accordingly, each of the aerial vehicles may operate, in crosswindflight, according to its respective flight path included in thedetermined asynchronous flight pattern.

In an exemplary embodiment, FIG. 7A illustrates the power profiles ofthe two aerial vehicles of the system 500, which may be operatingaccording to a determined asynchronous flight pattern. As illustrated inFIG. 7A, the power profiles of the aerial vehicles are substantially 180degrees out of phase with relative to one another. Thus, one aerialvehicle may be generating peak power as the other vehicle is generatingminimum power. Accordingly, the peak power that may flow through thesystem may be limited to the peak power generated by one aerial vehicle.As such, the grid components of the ground power unit may be sized tohandle at least the peak power of one aerial vehicle. Furthermore, asillustrated in FIG. 7A, the cumulative power profile 706 issubstantially regular.

The example provided in FIG. 7A and the accompanying description hereinis for illustrative purposes only and should not be considered limiting.For example, the power profile of each aerial vehicle may not besinusoidal, but may vary in other approximately periodic fashions. Asanother example, all points along the power profile 702 and 704 may notalways reflect generated power, but rather certain segments may resultin zero or negative power generation, i.e., glide or power consumption,in which power may be supplied to an aerial vehicle in order to maintainits respective flight path.

As another example, the phase difference between the two profiles may bea phase difference other than 180 degrees. In yet another example, thecumulative power profile 706 may not be uniform as illustrated in FIG.7A. In some embodiments, the cumulative power may vary, while thecumulative power profile is substantially regular. Accordingly, the peakpower that may flow through the system may be greater than the peakpower output of one aerial vehicle.

FIG. 7B illustrates the power profiles, 710, 712, and 714, of threeaerial vehicles connected to a shared ground power unit, according to anexemplary embodiment. As illustrated in FIG. 7B, the power profile ofeach aerial vehicle is substantially 120 degrees out of phase withrespect to the power profiles of the other two aerial vehicles. Thus,the peak power output of each aerial vehicle is 120 degrees out of phasewith respect to the peak power output of the other two aerial vehicles.Accordingly, although the peak power that may flow through the systemmay be greater than the peak power generated by one aerial vehicle, thepeak power is still much less than the possible peak power had the powergenerated by the each of the aerial vehicles been in phase.

Note that the example provided in FIG. 7B and the accompanyingdescription herein is for illustrative purposes only and should not beconsidered limiting. For example, the power profile of each aerialvehicle may not be sinusoidal, but may vary in other approximatelyperiodic fashions. As another example, all points along the powerprofiles may not always reflect generated power, but rather certainsegments may result in zero or negative power generation, i.e., glide orpower consumption, in which power may be supplied to an aerial vehiclein order to maintain its respective flight path. As another example, thephase difference between the three profiles may be a phase differenceother than 120 degrees. In yet another example, more than three AWTs maybe connected to a single common shared ground power unit.

Returning to the system 500, the peak power that may flow through theground power unit 514 may also increase when the aerial vehicle 504 andthe aerial vehicle 508 are deployed at the same time. Specifically, anaerial vehicle may require a power, which may be supplied by a groundpower unit, to be deployed. Accordingly, launching more than one aerialvehicle simultaneously may magnify the peak power that the electricalcomponents of the ground power unit may handle.

Therefore, in an embodiment, a plurality of aerial vehicles connected toa shared ground power unit may be deployed asynchronously to decreasethe peak power that may flow through the system. For example, in system500, each of the aerial vehicles 504 and 510 may be deployed in astaggered deployment order. As illustrated in FIG. 8, the aerial vehicle504 may be deployed into hover flight, while the aerial vehicle 510 isstill perched to the ground station 512. Furthermore, rather thanimmediately transitioning from hover flight to crosswind flight, theaerial vehicle 504 may transition to loitering flight.

Like in crosswind flight, an aerial vehicle in loitering flight may bepropelled by the wind substantially along a path, which as noted above,may convert kinetic wind energy to electrical energy. In someembodiments, the one or more propellers of the aerial vehicle maygenerate electrical energy by slowing down the incident wind. However,the flight path determination of an aerial vehicle may be than acrosswind flight path determination.

For example, the loitering flight path determination may be determinedsuch that the aerial vehicle flying in the loitering flight pathgenerates the same or substantially the same amount of power that itneeds to operate in loitering flight, which may result in zero ornear-zero load on the shared ground power unit. In an embodiment, thepower generated by the aerial vehicle as the aerial vehicle flies alongits loitering flight path may be used to directly provide the aerialvehicle with the power that it needs to operate in a loitering flight.In another embodiment, the aerial may include a rechargeable batterythat stores the power generated by the aerial vehicle as the aerialvehicle operates in a loitering flight. The power stored in therechargeable battery may subsequently be used to provide power to theaerial vehicle, which the aerial vehicle may require to fly in theloitering flight path.

In another example, the loitering flight path may be the crosswindflight path that an aerial vehicle flying the crosswind flight pathgenerates the least amount of power feasible in crosswind flight.Accordingly, the power that may flow from the aerial vehicle to theshared ground power unit may be decreased. In yet another example, theloitering flight path may be determined such that the aerial vehiclerequires the least amount of power from the shared ground power unitwhen flying along the determined loitering flight path. Accordingly, thepower that may flow from the shared ground power unit to the aerialvehicle may be decreased. In other examples, the loitering flight pathmay be determined such that the power from and/or to the aerial vehiclemay be decreased.

In an example, while the aerial vehicle 504 is in loitering flight, theaerial vehicle 510 may deploy and also enter loitering flight. Afterboth aerial vehicles are in loitering flight, the aerial vehicles maytransition into crosswind flight to generate electrical power. Thus, bystaggering the deployment of the aerial vehicles, the peak power thatmay flow through the ground power unit 514 may be substantially limitedto the peak power required to deploy a single aerial vehicle.

In another example, aerial vehicle 510 may deploy into crosswind flightwhile aerial vehicle 504 is in loitering flight. Subsequently, aerialvehicle 504 may transition from loitering flight to crosswind flight.The transition from loitering flight to crosswind flight may include atleast determining a crosswind flight path for an aerial vehicle. Thetransition from loitering flight to crosswind flight may also include anasynchronous flight path determination for the aerial vehicles.

FIG. 9 is a flowchart of an example process 900 for deploying two ormore aerial vehicles. Illustrative methods, such as method 900, may becarried out in whole or in part by a component or components of at leastone of the two or more aerial vehicles, such as by the one or morecomponents of the aerial vehicle 230 shown in FIG. 2 and the groundstation 210 shown in FIG. 2. For instance, method 900 may be performedby the control system 248 or by processor 212 shown in FIG. 2. However,it should be understood that example methods, such as method 900, may becarried out by other entities or combinations of entities withoutdeparting from the scope of the disclosure.

As shown by block 902, method 900 involves determining a deploymentorder for two or more aerial vehicles. The ground stations of the aerialvehicles may be connected to a shared ground power unit. The processor212 of the ground station 210 of each aerial vehicle may communicatewith the other ground stations using communication system 218.

Accordingly, at least one processor 212 of the ground stations maydetermine the deployment order. In some embodiments, the processor 212may communicate with the other AWTs to determine which AWTs will beactivated to generate power to determine which AWTs will be included inthe deployment order. In some examples, the deployment order may dependat least the location of each AWT connected to the shared ground powerunit or the current and/or projected weather conditions. In otherexamples, the deployment order may be predetermined and stored in datastorage 214 of at least one of the AWTs. In yet other examples, thedeployment order may be communicated to at least one AWT from anoperator the power generating system. Other considerations may be usedto determine the deployment order.

In response to the determination made at block 902, the processor 212may subsequently assign the deployment order to the aerial vehicles, asshown by block 904. For example, the processor 212 may communicate eachaerial vehicle's specific deployment order to each aerial vehicle'srespective ground station via communication system 218.

As shown by block 906, the first aerial vehicle in the assigneddeployment order may be deployed into hover flight as described in FIG.3 with respect to example 300. However, rather than transitioningimmediately from hover flight to crosswind flight after being deployed,the first deployed aerial vehicle may transition from hover flight intoloitering flight. Within examples, the transition from hover flight toloitering flight may be similar to the transition from hover flight tocrosswind flight, which is described above.

Further, as shown by block 908, for each aerial vehicle in the assigneddeployment order between the first aerial vehicle in the deploymentorder and the last aerial vehicle in the deployment order, the aerialvehicle determines that the preceding aerial vehicle in the assigneddeployment order is operating in loitering flight. Specifically, theground station of each subsequent aerial vehicle may communicate withthe ground station of the aerial vehicle immediately preceding it inorder to determine whether its aerial vehicle is operating in loiteringflight. If the aerial vehicle immediately preceding it is operating inloitering flight, the aerial vehicle may deploy into hover flight. Theaerial vehicle may then transition from hover flight into loiteringflight.

Finally, the last aerial vehicle in the assigned deployment orderdetermines whether the aerial vehicle preceding it in the assigneddeployment order is operating in loitering flight. If the aerial vehicleimmediately preceding it is operating in loitering flight, the aerialvehicle may deploy into hover flight. The aerial vehicle may thentransition from hover flight into crosswind flight. Subsequently, theaerial vehicles may transition to crosswind flight to generateelectrical power. In another example, all of the aerial vehicles maydeploy, according to a staggered deployment order, into loiteringflight. Subsequently, the aerial vehicles may transition into crosswindflight.

Accordingly, two or more aerial vehicles coupled to a shared groundpower unit may be deployed asynchronously, such that the peak power thatmay flow through the system during deployment of the aerial vehicles issubstantially the peak power required to deploy a single aerial vehicle.The costs of at least the grid components of such a system may besubstantially decreased. Other costs may be reduced as the capacity ofthe back-up batteries in the battery system may be reduced. As theaerial vehicles connected to a shared ground power unit may be deployedasynchronously, the back-up battery may need to provide power only to asingle aerial vehicle at a given time, and thus the batteries' capacitymay be reduced.

Furthermore, as explained above, two or more aerial vehicles operatingin crosswind flight may fly in a determined asynchronous flight pattern.As the two or more aerial vehicles fly in the determined asynchronousflight pattern, variable environmental conditions, such as changing windspeed, may cause one or more of the aerial vehicles to flight out of itsdetermined pattern according to the determined asynchronous flightpattern. The one or more aerial vehicles that may not be flyingaccording to their determined pattern relative to the other aerialvehicles may be referred to as “out-of-sync” aerial vehicles, whereasthe aerial vehicles flying according to the determined flight patternmay be referred to as “in-sync” aerial vehicles. Further, the powerprofile of an out-of-sync aerial vehicle may shift to become in phasewith power profile of at least one of the other aerial vehicles. As aresult, the power profile of the out-of-sync aerial vehicle may nolonger be out of phase with respect to the power generated by the otheraerial vehicles that are flying in the determined asynchronous pattern.

Consequently, the peak power that may flow through the system may exceedthe rated power of the electrical components, which may result in thefailure of at least some of the electrical components in the system.Also, the cumulative power profile may fluctuate, and thus may not meetthe demands of the electric grid.

Accordingly, at least the one or more out-of-sync aerial vehicles mayadjust one or more of their flight settings to resynchronize with thein-sync aerial vehicles. FIG. 10 illustrates a method 1000 of resyncingthe one or more out-of-sync aerial vehicles with the in-sync aerialvehicles, according to an exemplary embodiment. Illustrative methods,such as method 1000, may be carried out in whole or in part by acomponent or components of at least one of the two or more aerialvehicles, such as by the one or more components of the aerial vehicle230 shown in FIG. 2 and the ground station 210 shown in FIG. 2. Forinstance, method 1000 may be performed by the control system 248 shownin FIG. 2. However, it should be understood that example methods, suchas method 1000, may be carried out by other entities or combinations ofentities without departing from the scope of the disclosure.Furthermore, the control system may periodically perform the method1000. For example, the control system may periodically perform themethod 1000 every second. Other periodicities may be possible.

As shown by block 1002, the method 1000 includes determining that one ormore of the aerial vehicles are out-of-sync with the other aerialvehicles. In some embodiments, the control system of each aerial vehiclemay monitor the respective position and flight path of the other aerialvehicles connected to the shared ground power unit in order to determinewhether one or more of the aerial vehicles are out-of-sync. The controlsystem of each aerial vehicle may receive the position and/or operatingconditions of the other aerial vehicles from its ground station. Notethat the avionics of each aerial vehicle may be located on the aerialvehicle itself, and thus each respective control system mayindependently control its respective aerial vehicle.

Accordingly, the control system of the out-of-sync aerial vehicle maydetermine that its aerial vehicle is flying out-of-sync when the flightpattern of one of the aerial vehicle may not be operating according tothe determined asynchronous pattern. In other embodiments, the controlsystem may detect a significant change to its flight pattern due toenvironmental conditions, which may indicate that the aerial vehicle maybe out-of-sync. In yet other embodiments, the control system of anaerial vehicle may continuously and/or periodically monitor the phasedifferential between the power profile of the aerial vehicle and thepower profiles of the other aerial vehicles. If the phase differentialis outside a determined margin of error from a preferred phasedifferential, the control system of the aerial vehicle may determinethat the aerial vehicle is out-of-sync. Other criteria may be used todetermine that an aerial vehicle is out-of-sync.

In response to the control system of an aerial vehicle determining thatits aerial vehicle is out-of-sync, the control system may determine oneor more flight settings adjustments for the aerial vehicle. In someembodiments, the control system may use the position and/or operatingconditions of the other aerial vehicles to determine the flight settingadjustments to be made to the out-of-sync aerial vehicle.

Within examples, the control system of the out-of-sync aerial vehiclemay adjust at least the aerial vehicle's flight path in order to adjustthe characteristics of the power profile of the aerial vehicle. Forexample, the control system may adjust the aerial vehicle's flight pathby adjusting the perimeter of the flight path. More specifically,adjusting the aerial vehicle's perimeter may adjust at least thefrequency of the power profile of the aerial vehicle. For example, thefrequency of power profile generated by an out-of-sync aerial vehiclemay be adjusted to match the frequency of the power profiles of one ormore of the other aerial vehicles.

In another embodiment, an aerial vehicle may have a determined high windflight path and a determined low wind flight path, which mayrespectively correspond to the largest perimeter flight path and thesmallest perimeter flight path for the aerial vehicle. The controlsystem of the aerial vehicle may determine an adjusted flight path forthe out-of-sync aerial vehicle such that the flight path is a “blend” ofthe high wind flight path and the low wind flight path. The “blended”flight path may be determined such that the aerial vehicle's powerprofile has the same frequency as the power profiles of the other aerialvehicles.

However, in some embodiments, although the out-of-sync the power profileof the aerial vehicle has the same frequency as the other aerialvehicles, the phase of the power profile relative to at least one of theother power profiles may not be a preferred phase of the system.Consequently, the control system may adjust one or more other settingsof the aerial vehicle to adjust the phase of the power profile of theaerial vehicle relative to another aerial vehicle. Within examples, thecontrol system of the aerial vehicle may make an adjustment to thevelocity of the aerial vehicle in order to shift the phase of the powerprofile of the aerial vehicle. Within examples, any one of the aerialvehicle's drag, lift, or position of its flight path may be adjusted tomake an adjustment to the velocity of the aerial vehicle. Adjustments tothe other flight settings to make an adjustment to the velocity of anaerial vehicle may be possible.

In an example, the control system of the aerial vehicle may shift thephase of an aerial vehicle's power profile by adjusting the dragopposing the aerial vehicle, which may make an adjustment to thevelocity of the aerial vehicle. For instance, the drag on the aerialvehicle may be adjusted by changing the RPM of the aerial vehicle'smotors. Decreasing the RPM of the aerial vehicle's motors may increasethe drag on the aerial vehicle. Consequently, the velocity of the aerialvehicle may decrease, which may shift the phase of the power profilebackwards. Conversely, increasing the RPM of the aerial vehicle's motorsmay decrease the drag on the aerial vehicle, which may increase thevelocity of the aerial vehicle. Increasing the velocity of the aerialvehicle may shift the phase of the power profile forward. In otherexamples, the drag may be adjusted by adjusting the control surfaces ofthe aerial vehicle as explained elsewhere herein.

In another example, the control system may adjust the phase of the powergenerated by the aerial vehicle by adjusting at least the position ofthe flight path of the aerial vehicle. For example, the control systemmay move the center of the flight path off of downwind. In someexamples, determining the center of the flight path may includedetermining a wind speed of apparent wind-flow being applied to theaerial vehicle. Based on the wind speed of the apparent wind-flow beingapplied to the aerial vehicle the center of the flight path may bedetermined. More specifically, for example, the control system maydetermine the relative wind speed of the apparent wind-flow beingapplied to the aerial vehicle.

Based on the determination, the control system may determine a variationangle and using the variation angle may vary the adjusted flight path ina manner such that the adjust flight path is varied from the originalflight path at the variation angle. Thus, the adjusted flight path maybe varied from being substantially downwind of the ground station. Thevelocity of the aerial vehicle in the adjusted flight path location maybe different than the velocity of the aerial vehicle in the originalflight path location. Note that the settings may be changed for aspecified period of time. For example, the velocity of the aerialvehicle may be adjusted momentarily to shift the phase of the powerprofile of the aerial vehicle.

Alternatively, rather than adjusting the flight settings of only theout-of-sync aerial vehicles, the control system of each of the aerialvehicles connected to the shared ground power unit may adjust one ormore of their flight settings such that the aerial vehicles fly in-syncin an adjusted asynchronous pattern. Thus, the power profiles of theaerial vehicles flying in the adjusted asynchronous pattern may be outof phase with respect to each other. Further, each aerial vehicle maypredict, based on the environmental conditions for instance, how theother aerial vehicles may adjust their flight settings. Each aerialvehicle may use the prediction to determine any adjustments that mightbe made to its flight settings. In other examples, the control system ofat least one of the aerial vehicles (may be an aerial vehicle in-sync),may adjust one or more of its flight settings such that the aerialvehicles may fly according to a determined asynchronous pattern.

In an example, as shown in FIGS. 11A and 11B, two aerial vehicles(aerial vehicle 510 and aerial vehicle 504 of system 500) may beoperating in crosswind flight respectively along flight paths 1106 and1108. FIG. 11A illustrates an isometric view of aerial vehicles 504 and510 operating in crosswind flight orientation respectively along flightpaths 1106 and 1108 from a perspective that is above and behind groundstations 506 and 512.

As illustrated in FIG. 11A, the aerial vehicles are operating accordingto a determined asynchronous flight pattern. More specifically, theaerial vehicle 504 may be generating substantially peak power whileflying at the bottom of its flight path 1106. Simultaneously, the aerialvehicle 510 may be generating minimum power while flying at the top ofits flight path 1108. However, as explained above, at least one of theaerial vehicles 504 and 510 may experience changing environmentalconditions that may cause one of the aerial vehicles to fly out-of-syncwith the other aerial vehicle.

In this example, changing wind conditions cause the aerial vehicle 504to fly out-of-sync with the aerial vehicle 510 (i.e. the aerial vehicle504 is not flying according to the determined asynchronous pattern).Accordingly, the control system of the aerial vehicle 504 may detectthat the aerial vehicle 504 is out-of-sync. Likewise, the control systemof the aerial vehicle 510, which is receiving aerial vehicle 504'spositioning information, may detect that the aerial vehicle 504 isflying out-of-sync. As a result of aerial vehicle 504 flyingout-of-sync, the phase of the power profile of the aerial 504 is shiftedforward relative to the power profile of the aerial vehicle 510, whichmay cause the power profiles of the aerial vehicles to be in-phase.

In response to detecting that the aerial vehicle 504 is out-of-sync, thecontrol system of each aerial vehicle may adjust one or more flightsettings such that the aerial vehicles 504 and 510 fly in-sync. In someexamples, at least one of the aerial vehicles may adjust one or moreflight settings such that the aerial vehicles fly according to theoriginal determined asynchronous flight pattern. In other examples, atleast one of the aerial vehicles may adjust one or more flight settingssuch that the aerial vehicles fly according to an updated asynchronousflight pattern. For instance, an updated asynchronous flight pattern maybe determined based on a preferred phase differential between the powerprofiles of each of the aerial vehicles.

In the example of FIG. 11, both aerial vehicle 504 and 510 may adjustone or more of flight settings such that the phase between the powerprofiles of each aerial vehicle is substantially the preferred phase.More specifically, the control system of the aerial vehicle 504 mayadjust at least the perimeter of the aerial vehicle 504's flight path1108 to adjust the frequency of the power profile of the aerial vehicle.As illustrated in FIG. 11B, the control system of the aerial vehicle mayincrease the perimeter of the flight path 1108 such that the adjustedflight path 1118 is wider, which may adjust the frequency of the powerprofile as explained above. Subsequently, the control system maymomentarily adjust the velocity of the aerial vehicle, using methodsdescribed herein, to shift the phase of the power profile back.

Furthermore, the control system of the aerial vehicle 510 may alsodecrease the perimeter of the flight path 1106 such that the adjustedflight path 1120 is narrower. As explained above, decreasing theperimeter of the flight path 1106 may adjust the frequency of the powerprofile of the aerial vehicle 1102. Subsequently, the control system maymomentarily adjust the velocity of the aerial vehicle 1102, usingmethods described herein, to shift the phase of the power profileforward. Accordingly, the aerial vehicles may be flying in-sync suchthat the phase between the power profiles of the aerial vehicles is thedetermined preferred phase differential.

The example provided in FIG. 11 and the accompanying description hereinis for illustrative purposes only and should not be considered limiting.For example, more than two aerial vehicles may be included in system500. As another example, the aerial vehicle may have flight pathsdifferent than the flight paths illustrated in FIG. 11.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims.

The above detailed description describes various features and functionsof the disclosed systems, devices, and methods with reference to theaccompanying figures. In the figures, similar symbols typically identifysimilar components, unless context dictates otherwise. The exampleembodiments described herein and in the figures are not meant to belimiting. Other embodiments can be utilized, and other changes can bemade, without departing from the spirit or scope of the subject matterpresented herein. It will be readily understood that the aspects of thepresent disclosure, as generally described herein, and illustrated inthe figures, can be arranged, substituted, combined, separated, anddesigned in a wide variety of different configurations, all of which areexplicitly contemplated herein.

A block that represents a processing of information may correspond tocircuitry that can be configured to perform the specific logicalfunctions of a herein-described method or technique. Alternatively oradditionally, a block that represents a processing of information maycorrespond to a module, a segment, or a portion of program code(including related data). The program code may include one or moreinstructions executable by a processor for implementing specific logicalfunctions or actions in the method or technique. The program code and/orrelated data may be stored on any type of computer readable medium suchas a storage device including a disk or hard drive or other storagemedium.

The computer readable medium may also include non-transitory computerreadable media such as computer-readable media that stores data forshort periods of time like register memory, processor cache, and randomaccess memory (RAM). The computer readable media may also includenon-transitory computer readable media that stores program code and/ordata for longer periods of time, such as secondary or persistent longterm storage, like read only memory (ROM), optical or magnetic disks,compact-disc read only memory (CD-ROM), for example. The computerreadable media may also be any other volatile or non-volatile storagesystems. A computer readable medium may be considered a computerreadable storage medium, for example, or a tangible storage device.

Moreover, a block that represents one or more information transmissionsmay correspond to information transmissions between software and/orhardware modules in the same physical device. However, other informationtransmissions may be between software modules and/or hardware modules indifferent physical devices.

The particular arrangements shown in the figures should not be viewed aslimiting. It should be understood that other embodiments can includemore or less of each element shown in a given figure. Further, some ofthe illustrated elements can be combined or omitted. Yet further, anexample embodiment can include elements that are not illustrated in thefigures.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopebeing indicated by the following claims.

We Claim:
 1. A method comprising: determining an asynchronous flightpattern for two or more aerial vehicles coupled to a ground station,wherein the asynchronous flight pattern comprises a respective flightpath for each of the two or more aerial vehicles, and wherein the groundstation is coupled to a common shared ground power unit; and operatingeach of the aerial vehicles in a crosswind flight substantially alongits respective flight path, wherein each aerial vehicle generateselectrical energy over time in a periodic profile, and wherein theprofile of each aerial vehicle is out of phase with respect to eachprofile of the other aerial vehicles.
 2. The method of claim 1 furthercomprising: while the aerial vehicles are operating in the crosswindflight: determining that the flight pattern of one of the aerialvehicles is not operating according to the determined asynchronouspattern relative to at least one other aerial vehicle; responsive to thedetermination, determining one or more adjusted flight settings for atleast one of the aerial vehicles; and operating the at least one aerialvehicle according to the one or more adjusted flight settings.
 3. Themethod of claim 2, wherein the adjusted flight settings change the phaseof the periodic power profile generated by the at least one aerialvehicle relative to the periodic profile generated by at least one otheraerial vehicle.
 4. The method of claim 2, wherein the adjusted flightsettings change the frequency of the periodic power profile generated bythe at least one aerial vehicle.
 5. The method of claim 2, wherein theone or more adjusted flight settings comprise a different flight path ofthe at least one aerial vehicle.
 6. The method of claim 2, wherein theone or more adjusted flight settings comprise adjustments to thevelocity of the at least one aerial vehicle.
 7. A method comprising:determining at least one preferred phase differential between periodicpower profiles generated by two of two or more aerial vehicles coupledto a ground station, wherein the ground station is coupled to a sharedground power unit; based at least on the at least one preferred phasedifferential, determining an asynchronous flight pattern for the aerialvehicles, wherein the determined asynchronous flight pattern comprises arespective flight path for each of the aerial vehicles; operating eachof the aerial vehicles in a crosswind flight substantially along itsrespective flight path, wherein each aerial vehicle generates electricalpower over time in a periodic profile, and wherein a phase differentialbetween the power profiles generated by two of the aerial vehicles issubstantially the preferred phase differential.
 8. The method of claim 7further comprising: while the aerial vehicles are operating in thecrosswind flight: determining that the flight pattern of one of theaerial vehicles is not operating according to the determinedasynchronous flight pattern relative to at least one other aerialvehicle; responsive to the determination, determining at least oneadjusted preferred phase differential; based on the at least oneadjusted preferred phase differential, determining one or more adjustedflight settings for at least one of the two or more aerial vehicles; andoperating the at least one aerial vehicle according to the one or moreadjusted flight settings.
 9. The method of claim 8, wherein the adjustedflight settings change the phase of the periodic power profile generatedby the at least one aerial vehicle relative to the periodic profilegenerated by at least one other aerial vehicle.
 10. The method of claim7 further comprising: while the aerial vehicles are operating in thecrosswind flight: determining that the flight pattern of one of theaerial vehicles is not operating according to the determinedasynchronous flight pattern relative to at least one other aerialvehicle; responsive to the determination, determining one or moreadjusted flight settings for at least one of the aerial vehicles; andoperating the at least one aerial vehicle according to the one or moreadjusted flight settings.
 11. A method comprising: determining adeployment order for two or more aerial vehicles coupled to a groundstation, wherein each aerial vehicle is configured to operatesubstantially along a respective flight path to generate electricalpower, and wherein the ground station is coupled to a shared groundpower unit; assigning the deployment order to the two or more aerialvehicles; deploying the two or more aerial vehicles according to theassigned deployment order, wherein deploying the two or more vehiclesaccording to the assigned deployment order comprises: for an aerialvehicle in a first position of the deployment order, (i) deploying theaerial vehicle, (ii) operating the aerial vehicle in a loitering flight;for each aerial vehicle in the assigned deployment order between theaerial vehicle in the first position of the deployment order and anaerial vehicle in a last position of the deployment order, (i)determining that the preceding aerial vehicle in the assigned deploymentorder is operating in the loitering flight, (ii) deploying the aerialvehicle (iii) operating the aerial vehicle in a loitering flight; forthe aerial vehicle in the last position of the deployment order,(i)determining that the preceding aerial vehicle in the assigneddeployment order is operating in the loitering flight, (ii) deployingthe aerial vehicle, (iii) operating the aerial vehicle in a crosswindflight.
 12. The method of claim 11, wherein operating the aerial vehiclein the loitering flight comprises: determining a respective loiteringflight path for the aerial vehicle; operating the aerial vehicleaccording to its respective loitering flight path, wherein the aerialvehicle operating according to its respective loitering flight pathgenerates a power, wherein the generated power is substantiallyequivalent to a power needed to operate the aerial vehicle in theloitering flight.
 13. The method of claim 11 further comprising:determining that the aerial vehicle in the last position of thedeployment order is operating in the crosswind flight; responsive to thedetermination, operating the aerial vehicles in a crosswind flight. 14.A non-transitory computer readable medium having stored thereininstructions executable by one or more processors to cause a computingsystem to perform functions comprising: determining an asynchronousflight pattern for two or more aerial vehicles coupled to a groundstation, wherein the asynchronous flight pattern comprises a respectiveflight path for each of the two or more aerial vehicles, and wherein theground station is coupled to a common shared ground power unit; andoperating each of the aerial vehicles in a crosswind flightsubstantially along its respective flight path, wherein each aerialvehicle generates electrical energy over time in a periodic profile, andwherein the profile of each aerial vehicle is out of phase with respectto each profile of the other aerial vehicles.
 15. The non-transitorycomputer readable medium of claim 14, the functions further comprising:while the aerial vehicles are operating in the crosswind flight:determining that the flight pattern of one of the aerial vehicles is notoperating according to the determined asynchronous pattern relative toat least one other aerial vehicle; responsive to the determination,determining one or more adjusted flight settings for at least one of theaerial vehicles; and operating the at least one aerial vehicle accordingto the one or more adjusted flight settings.
 16. The non-transitorycomputer readable medium of claim 15, wherein the adjusted flightsettings change the phase of the periodic power profile generated by theat least one aerial vehicle relative to the periodic profile generatedby at least one other aerial vehicle.
 17. The non-transitory computerreadable medium of claim 15, wherein the adjusted flight settings changethe frequency of the periodic power profile generated by the at leastone aerial vehicle.
 18. The non-transitory computer readable medium ofclaim 15, wherein the one or more adjusted flight settings comprise adifferent flight path of the at least one aerial vehicle.
 19. Thenon-transitory computer readable medium of claim 15, wherein the one ormore adjusted flight settings comprise adjustments to the velocity ofthe at least one aerial vehicle.
 20. The non-transitory computerreadable medium of claim 14, the functions further comprising:determining a deployment order for the two or more aerial vehicles;assigning the deployment order to the two or more aerial vehicles; anddeploying the two or more aerial vehicles according to the assigneddeployment order.